This invention relates to sulfur cement-aggregate compositions. In a further aspect, the invention relates to sulfur mortars and concretes containing an aggregate which is contaminated with a water-expansive clay.
Sulfur mortars and concretes generally refer to a mixture of sulfur and aggregate wherein the sulfur functions as the cement or binder. Generally, whether a composition is classed as a mortar or concrete is based on the particle size of the predominate aggregate. Thus, compositions containing larger sized aggregates are generally referred as concretes whereas compositions containing smaller sized aggregate are referred to as mortars. In either case, the compositions can also contain very fine particle size aggregates, such as fly ash, etc., as fillers. Sulfur mortars and concretes are prepared by heating sulfur with an aggregate at a sufficient temperature to render the sulfur molten and then allowing the mixture to cool to solidify the sulfur. Not infrequently, the sulfur also contains a plasticizer which desirably increases the cold plasticity crystallization time of the sulfur, probably by reacting with at least a portion of the sulfur. Such sulfur is referred to as plasticized sulfur.
Sulfur mortars and concretes can be broadly classified as sulfur cement products. Sulfur cement is similar to Portland cement in forming concretes or mortars. In the latter case, a mixture of Portland cement and aggregate is solidified into a final solid product by treatment with water. In the case of sulfur products, heat is used to render the sulfur cement molten, which, upon cooling, solidifies, binding the aggregate.
Sulfur cement concretes can be used for many of the same purposes as conventionally formed concretes. For example, sulfur concretes can be used for structural members, roads, slabs, curbings, gutters, and can be precast or cast at the job site. Sulfur cement concrete affords a significant advantage over Portland cement concrete, especially in the case of preformed articles, in that the sulfur cement concrete can be remelted and recast. Thus, when defective or surplus articles are prepared, the sulfur aggregate composition can be reused by merely melting down the article and recasting the composition. Suflur cement mortars can be used for similar purposes as Portand cement mortars, such as, for example, bonding structural members together. Sulfur cement mortars and concretes also generally have good corrosion resistance to acids and other chemicals.
U.S. Pat. No. 3,440,064 discloses sulfur compositions and teaches that incorporation therein of styrene or an alkyl mercaptan in combination with a broad range of other additives, including certain unsaturated carboxylic acids improves flame retardancy.
Sulfur cement mortars and concretes are well-known to the art and various modifications are, for example, described in the patent literature, for example, U.S. Pat. Nos. 2,135,747, 3,954,480, 4,025,352, 4,058,500, and 4,118,230.
One of the disadvantages of sulfur cement mortars and concretes is that the presence of small amounts of water-expansive clay (for example, 1% by weight or more) in the aggregate causes the solidified sulfur cement mortars and concretes to disintegrate when exposed to water. This problem is particularly serious since, because of transportation costs, economic necessity usually requires the use of aggregate sources close to the casting or job site, regardless of the presence of expansive clay. The expansive clay can be removed from the aggregate by washing procedures but such procedures are also generally inconvenient and uneconomical. Thus, if the local sources of aggregate contain expansive clay, the use of sulfur cement mortars and concretes is pragmatically severely restricted.
U.S. Pat. No. 4,188,230 teaches that this problem may be obviated by the incorporation of petroleum or polyol additives. Such procedures have not, in fact, proved entirely satisfactory. The problem of water-expansive clays was also considered in an article by Shrive, Gillott, Jordaan and Loov, appearing at Page 484 of the Journal of Testing and Evaluation (1977). In this article, the results of certain experiments with water-expansive clays are described. In these experiments, a mixture containing 3 parts, by volume, fly ash, and 2 parts bentonite clay were slurried with water. Batches of this slurry were, respectively, mixed with aqueous solutions containing 1% and 5% by weight calcium hydroxide or potassium chloride and allowed to stand overnight. Sulfur cement samples were prepared by slowly adding the slurries (to evaporate water) to molten sulfur. The final samples contained 75:15:10 parts by volume of sulfur:fly ash:bentonite clay. Samples of the treated and untreated materials were immersed in water after setting for 1 day and 7 days. Both the treated and untreated samples disintegrated within 3 or 4 hours of immersion and accordingly the investigation was discontinued.
U.S. Pat. Nos. 4,332,911 and 4,332,912 disclose methods for increasing the water stability of sulfur cement-aggregate compositions containing water-expansive clay, which comprises adding particulate soluble salts to the aggregate or treating the aggregate with salt solutions.